A method and system for analyzing partial insulation degradation of a cable joint

Abstract

The application discloses a method and system for analyzing partial insulation aging of a cable joint, and comprises the following steps: S1, acquiring thermal behavior of an insulation assembly by using an infrared imager; and S2, according to the thermal behavior of the insulation assembly, distinguishing differences in temperature change rates of different regions based on temperature rise changes of specific observation points in each time period, so as to detect partial insulation aging.

Description

Technical Field

[0001] This invention belongs to the technical field of cable T-joints, and particularly relates to a method and system for analyzing local aging of cable joint insulation. Background Technology

[0002] As the cornerstone of modern society, the power system supports social and economic development, and its safe and stable operation is a critical priority. Among its many components, cable T-joints are essential for maintaining reliable connections within the power network. However, the aging of the insulation material in these joints poses a significant threat to system reliability, as insulation degradation can trigger abnormal temperature responses, impairing performance and safety. Cross-linked polyethylene (XLPE), a commonly used material for high-voltage cable insulation, plays a crucial role in ensuring the durability and reliability of the power system. Maintaining the integrity of XLPE insulation is extremely important for reducing the risks associated with insulation aging, thereby ensuring the stability, safety, and efficiency of the entire power system.

[0003] Examples of insulation breakdown in cable joints highlight the risks posed by insulation aging. For instance, the scale of the problem is clearly evident in two wind farms in Hubei Province. At Wind Farm A, since its commissioning in October 2019, the T-connectors in the prefabricated substation have experienced 11 insulation breakdown and explosion incidents. Similarly, Wind Farm B has experienced eight such incidents since its commissioning in March 2019. These failures typically lead to emergency shutdowns of affected equipment, resulting in prolonged outages, and in severe cases, jeopardizing not only the wind turbines but also the safety and stability of the entire power grid. Such disruptions underscore the urgent need to study cable joint failure mechanisms, implement real-time monitoring systems, and provide early warnings to prevent failures. Addressing these issues can ensure the safety and reliability of power transmission from wind farms and guarantee uninterrupted grid operation. Traditionally, monitoring insulation aging in T-connectors relies on periodic offline inspections or post-failure analysis. These methods encompass visual inspection of surface wear, measurement of insulation resistance, or partial discharge (PD) testing to assess the overall condition of the insulation. While these technologies can identify obvious faults, they are inherently passive and have limited ability to predict early aging or provide continuous monitoring.

[0004] Currently, maintenance practices typically involve on-site inspections by operations and maintenance (O&M) personnel or real-time diagnostics using online monitoring systems. These systems are highly effective in responding quickly to incidents or predicting damage caused by abnormal operating conditions. However, they often fall short in detecting progressive aging under normal operating conditions, especially before damage reaches a critical threshold. This limitation makes preventative maintenance difficult and leaves systems vulnerable to sudden failures.

[0005] Despite the variety of existing power cable monitoring technologies, current methods have significant limitations. Many methods struggle to provide continuous, real-time monitoring, making it difficult to detect early aging, especially in localized areas prone to thermal degradation. The subtle temperature changes caused by localized aging are often imperceptible, delaying the identification of potential fault points and increasing the likelihood of catastrophic failures.

[0006] Most research and maintenance work focuses on XLPE cable joints, with limited attention paid to T-joints. However, cable T-joints play an indispensable role in switchgear, serving as critical incoming and outgoing components that significantly impact the safety and efficiency of power production systems. Despite their relatively low individual cost, failures in these joints can lead to serious economic and social consequences, including substantial downtime losses and risks to system reliability. The complex structure of T-joints often causes thermal stress concentration at the cable joint and the fracture points between the insulation and shielding layers within the joint, making them highly susceptible to performance degradation over long-term operation. However, research on the phenomenon of T-joints suddenly and unexpectedly cracking after many years of normal operation remains scarce and urgently requires further in-depth investigation. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method and system for analyzing local aging of cable joint insulation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for analyzing localized aging of cable joint insulation includes:

[0010] Step S1: Obtain the thermal behavior of the insulating components;

[0011] Step S2: Based on the thermal behavior of the insulating components, identify the differences in the rate of temperature change in different regions based on the temperature rise changes at specific observation points within each time period.

[0012] Preferably, an infrared imager is used to perform infrared imaging on the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

[0013] Preferably, the temperature rise at a specific observation point is obtained based on the temperature difference between the thick and thin layers of the insulation component and the insulation aging threshold.

[0014] Preferably, the insulating components are divided into multiple regions, each equipped with an infrared imager, and the S value for each region is calculated. i The rate of temperature change is calculated using the following formula:

[0015]

[0016] ΔT i (t)=T i (t+△t)-T i (t)

[0017] Where, ΔT i For the Sth i Temperature change at a point over time; ΔT i (t) represents the Sth... i The temperature difference at different times; Δt represents the time interval;

[0018] By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

[0019] The present invention also provides a system for analyzing localized aging of cable joint insulation, comprising:

[0020] A data acquisition device is used to obtain the thermal behavior of insulating components;

[0021] An analytical device is used to identify differences in the rate of temperature change in different regions based on the thermal behavior of insulating components and the temperature rise at a specific observation point within each time period.

[0022] Preferably, the acquisition device uses an infrared imager to perform infrared imaging on the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

[0023] Preferably, the temperature rise at a specific observation point is obtained based on the temperature difference between the thick and thin layers of the insulation component and the insulation aging threshold.

[0024] Preferably, the insulating components are divided into multiple regions, each equipped with an infrared imager, and the S value for each region is calculated. i The rate of temperature change is calculated using the following formula:

[0025]

[0026] ΔT i (t)=T i (t+△t)-T i (t)

[0027] Where, ΔT i For the Sth i Temperature change at a point over time; ΔT i (t) represents the Sth... i The temperature difference at different times; Δt represents the time interval;

[0028] By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

[0029] This invention provides real-time monitoring and early detection of insulation aging in cable T-joints, with a focus on the thermal behavior of insulation components. This will pave the way for more accurate prediction models and more intelligent maintenance practices, ultimately ensuring the safe, reliable, and efficient operation of power systems. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating the method for analyzing localized aging of cable joint insulation according to an embodiment of the present invention;

[0032] Figure 2 This is a flowchart of the thermal aging analysis experiment. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1:

[0036] like Figure 1 As shown, this embodiment of the invention provides a method for analyzing localized aging of cable joint insulation, comprising:

[0037] Step S1: Obtain the thermal behavior of the insulation components using an infrared imager; wherein, the insulation components of the cable T-joint are imaged with infrared at predetermined intervals using an infrared imager to achieve continuous observation of temperature behavior.

[0038] Step S2: Based on the thermal behavior of the insulation component, the difference in temperature change rate in different regions is identified based on the temperature rise change at a specific observation point within each time period to detect local insulation aging; wherein, based on the temperature difference between the thick and thin layers of the insulation component, the temperature rise change at a specific observation point is obtained based on the insulation aging threshold; and the difference in temperature change rate in different regions is identified based on differential thermal analysis.

[0039] In one embodiment of the present invention, in step S1, an infrared imager is used as a temperature sensor to monitor critical insulation components in the power system that are prone to failure, such as cable T-joints. Infrared imaging is performed at regular intervals (typically several minutes to half an hour) to ensure continuous observation of temperature behavior. Analysis is conducted on the temperature rise at specific observation points within each time period to identify subtle differences in the rate of temperature change in different regions. Subsequently, based on the principle that the heat transfer rate decreases as the polymer degrades into smaller molecular structures, these changes are correlated with the aging process of the insulating polymer.

[0040] This temperature difference analysis is crucial for detecting localized insulation aging by observing rapidly changing temperature differences over time. Continuous monitoring of temperature changes in the cable T-joint area can reveal abnormal heating phenomena, a key indicator of aging. During long-term use, electrical and thermal stresses cause polymer degradation, altering its structure and slowing heat transfer. According to heat conduction theory, well-insulated sections efficiently transfer heat, while aged sections impede heat transfer due to material changes. This behavior aligns with the heat conduction equation, which describes the spatial and temporal changes in temperature within a material.

[0041]

[0042] Where T = T(x, y, z, t) represents temperature, which is a function of position (x, y, z) and time t, and α is the thermal diffusivity; defined as k is thermal conductivity; ρ is the density of the insulator; c p It is specific heat capacity; It is the Laplace operator, which describes the spatial variation of temperature in three-dimensional space, and its expression is:

[0043]

[0044] In one embodiment of the present invention, step S2 involves dynamically detecting the surface temperature of cable T-joints with different insulation thicknesses. This allows for the assessment of local and overall insulation aging conditions, enabling timely replacement when signs of aging appear. Thinner insulation layers in the T-joint respond more rapidly to temperature changes, while thicker insulation layers respond more slowly. The thinner cross-linked polyethylene (XLPE) insulation layer at the bottom of the T-joint conducts heat quickly, resulting in a rapid initial temperature rise, but the rate of temperature increase gradually slows down over time. Conversely, thicker insulation layers have a slower initial response, but their temperature rise gradually accelerates as heat accumulates within the T-joint cavity. This method emphasizes the importance of insulation thickness in determining temperature response and insulation aging.

[0045] Insulation aging threshold judgment:

[0046] The outer surface layer of a cable T-joint typically maintains a stable temperature with minimal variation. As long as the temperature rise remains below a set threshold, it indicates good insulation condition. Significant deviations from this pattern may indicate insulation aging, as temperature variation is directly related to the severity of aging. A temperature difference threshold derived from a well-insulated T-joint helps assess this aging condition. If the observed temperature difference exceeds this threshold, it indicates severe insulation aging, guided by a threshold equation.

[0047] Define temperature difference:

[0048] Determine the temperature T of the thick layer thick Determine the temperature T of the thin layer thin And the change in temperature difference is;

[0049] ΔT=T thick -T thin

[0050] Initial reference value

[0051] During the good insulation phase, the temperature difference between the thick and thin layers was measured and recorded:

[0052] ΔT ref =T thick,ref -T thin,ref

[0053] In subsequent monitoring, the current temperature difference ΔT will be continuously recorded. current And calculate the difference between it and the reference value. The relationship between the two is as follows:

[0054] ΔT diff =ΔT current -ΔT ref

[0055] Set a temperature difference threshold ΔT threshold If ΔTdiff Exceeding this threshold indicates severe insulation aging, and the judgment is as follows:

[0056] |ΔT diff |>ΔT threshold

[0057] In one embodiment of the present invention, in step S2, the present invention monitors the temperature changes in different areas of the T-joint by dividing the insulating component into multiple areas (e.g., (S1, S2, S3, S4, S5)), obtaining infrared images of each area, and calculating the temperature S of each area. i The rate of temperature change is calculated using the following formula:

[0058]

[0059] ΔT i (t)=T i (t+△t)-T i (t)

[0060] Where, ΔT i For the Sth i Temperature change at a point over time; ΔT i (t) represents the Sth... i The temperature difference at different times; Δt represents the time interval;

[0061] By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

[0062] Differential analysis highlights the variations in local heat transfer rates. The aging region dissipates heat more slowly, with a ΔT... i The lower values ​​directly indicate a degradation in insulation performance. In particular, the response time of the aged areas is significantly delayed compared to the new areas.

[0063] like Figure 2 As shown, the thermal aging analysis performed using the method of this invention includes:

[0064] 1. Set the target temperature inside the T-connector using a programmable heating device to simulate the working conditions of the T-connector or accelerate its aging. The typical target temperature range is 40℃~90℃. This range is chosen to represent normal operating conditions or for experimental purposes aimed at accelerating the aging process.

[0065] 2. Determine the initial internal and external temperatures. Before heating begins, measure the initial temperature of the T-joint to establish a baseline for further analysis. Thermocouples are used to measure the internal temperature, while an infrared imager records the surface temperature. Separate measurements are taken for thick and thin insulation layers to evaluate their baseline thermal behavior.

[0066] 3. Continuous monitoring during the heating process. The internal temperature of the T-joint and the temperatures of the thick and thin insulation layers are continuously measured and recorded periodically. Measurements are taken at consistent time intervals, for example, every 5 minutes during the experiment. These measurements are crucial for analyzing how heat is transferred through the T-joint over time.

[0067] 4. Cooling Stage: After heating, allow the T-joint to cool naturally, and record the temperature during this stage. The heat dissipation characteristics of the insulation layer are evaluated by analyzing the cooling rate. The difference in cooling behavior between thick and thin insulation layers provides insights into localized aging.

[0068] 5. Repeated experiments under three different settings:

[0069] 1) Conduct multiple sets of experiments under the following conditions:

[0070] The same T-connectors were used with the same setup: experiments were repeated to verify the repeatability and consistency of the results. Errors caused by instrument noise and environmental factors were analyzed.

[0071] 2) Same T-joint, different settings: Change parameters such as target temperature and heating time to study their effects on thermal response. The systematic error caused by parameter changes is quantified.

[0072] 3) T-joints with different service lives: Experiments were conducted on T-joints with different aging levels to compare their thermal response.

[0073] 6. Error handling and data cleaning

[0074] The recorded temperature data is processed to eliminate anomalies or outliers caused by sensor inaccuracies or environmental noise. Data cleaning includes techniques such as interpolation or smoothing. Measurement errors are quantified using statistical metrics such as standard deviation and root mean square error (RMSE).

[0075] 7. Aging assessment

[0076] Based on the processed data, differential temperature analysis was used to assess the aging degree of the T-joints. The relationship between the thermal gradient (ΔT) and the insulation degradation state was analyzed. A threshold (ΔT) was used to determine whether the insulation had reached a critical aging state.

[0077] 8. Warning signal or normal operation

[0078] If aging indicators are detected and severe insulation degradation is observed, a warning signal will be issued. If the insulation temperature difference is within an acceptable range, normal operation will continue.

[0079] Example 2:

[0080] This invention also provides a system for analyzing localized aging of cable joint insulation, comprising:

[0081] A data acquisition device is used to obtain the thermal response of insulating components;

[0082] An analytical device is used to identify differences in the rate of temperature change in different regions based on the thermal response of insulating components and the temperature rise at a specific observation point within each time period.

[0083] As one embodiment of the present invention, the acquisition device uses an infrared imager to perform infrared imaging on the insulation components of the cable T-joint at predetermined intervals to achieve continuous observation of temperature behavior.

[0084] As one embodiment of the present invention, the temperature rise change at a specific observation point is obtained based on the temperature difference between the thick and thin layers of the insulation component and the insulation aging threshold.

[0085] In one embodiment of the present invention, the insulating component is divided into multiple regions, and each region is equipped with an infrared imager to calculate S for each region. i The rate of temperature change is calculated using the following formula:

[0086]

[0087] ΔT i (t)=T i (t+△t)-T i (t)

[0088] Where, ΔT i For the Sth i Temperature change at a point over time; ΔT i (t) represents the Sth... i The temperature difference at different times; Δt represents the time interval;

[0089] By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing localized aging of cable joint insulation, characterized in that, include: Step S1: Obtain the thermal behavior of the insulating components; By using an infrared imager to perform infrared imaging on the insulation components of the cable T-joint at predetermined intervals, continuous observation of temperature behavior can be achieved. Step S2: Based on the thermal behavior of the insulation components, identify the differences in the rate of temperature change in different regions based on the temperature rise changes at specific observation points within each time period; Based on the temperature difference between the thick and thin layers of the insulation component, and judging based on the insulation aging threshold, the temperature rise at a specific observation point is obtained. Define temperature difference: Determine the temperature of the thick layer Determine the temperature of the thin layer And the change in temperature difference is: ； Initial reference value: During the good insulation phase, the temperature difference between the thick and thin layers was measured and recorded: ； In subsequent monitoring, the current temperature difference will be continuously recorded. And calculate the difference between it and the reference value. The relationship between the two is as follows: ； Set temperature difference threshold ,if Exceeding this threshold indicates severe insulation aging, and the judgment is as follows: ； By dividing the insulating components into multiple regions, each equipped with an infrared imager, the calculations for each region are obtained. S i The rate of temperature change is calculated using the following formula: ； ； in, For the first The change of temperature at a point over time; Indicates the first Temperature difference at different times; Indicates a time interval; By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

2. A system for analyzing the local aging of cable joint insulation, implementing the method for analyzing local aging of cable joint insulation as described in claim 1, characterized in that, include: A data acquisition device is used to obtain the thermal behavior of insulating components; An analytical device is used to identify differences in the rate of temperature change in different regions based on the temperature rise at a specific observation point within each time period, according to the thermal behavior of the insulating components. The data acquisition device uses an infrared imager to perform infrared imaging on the insulation components of the cable T-joint at predetermined intervals, thereby enabling continuous observation of temperature behavior. Based on the temperature difference between the thick and thin layers of the insulation component, and judging based on the insulation aging threshold, the temperature rise at a specific observation point is obtained. By dividing the insulating components into multiple regions, each equipped with an infrared imager, the calculations for each region are obtained. S i The rate of temperature change is calculated using the following formula: ； ； in, For the first The change of temperature at a point over time; Indicates the first Temperature difference at different times; Indicates a time interval; By comparing the differences between different areas of the same thickness, abnormal conditions in temperature changes can be identified.

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